This proposal is based on the premise that malformation of cranioskeletal structures during growth is influenced by alterations in muscle activity affecting bone remodeling and skeletal structure. It is suggested that modification of sensory input affecting reflexive pathways of the central nervous system alters this muscular activity. This investigation attempts to define some of the on-going changes in craniofacial muscle activity during development of predictable morphologic alterations in three experimental models utilizing rhesus monkeys. Paired animals in each model will receive intramuscular and surface electrodes in three muscles selected as representative of change in tone and activity. Analysis of EMG data is carried out by computer programs designed to compare results of one muscle under four conditions: 1) at resting level, 2) during increased load on the mandible, 3) during elicitation of the jaw opening reflex, and 4) in masticatory movements. The trend in intensity of EMG frequency of units in EMG, and discharge patterning of single motor units will be analyzed over successive recording sessions during the development of the morphologic alterations. At this point in time the work is concentrated on the experimental model for the study on oral respiration. A series of muscles, specially recruited for oral respiration, have been identified. The sequence of recruitment and the concomitant morphologic changes which result in dental malocclusion are being studied.